When a ship's hull is provided with a conventional rudder and the ship is subject to wave action causing the ship to roll, considerable lateral forces are applied to opposite sides of the ship's rudder tending to turn the rudder against the steering mechanism controlling the positioning of the rudder. In addition, conventional ships' rudders also experience excessive side thrusts when the ship is moving downwind through swells or waves and tends to yaw. Still further, single propeller hulls provided with conventional rudders are difficult to steer in one direction (determined by the direction of rotation of the ship's propeller) when moving astern and conventional ships' rudders do not confine any portion of the wash from the propeller with the result that a considerable portion of the rearward thrust developed by the propeller is expended laterally outwardly of the center line of the propeller in all directions thereabout. This, of course, results in inefficient operation and more fuel consumption.
Accordingly, a need exists for a ship's propeller which does not tend to drive the steering mechanism of the propeller when the ship is rolling or yawing and also for a rudder which offers greater steerage when the ship is operated astern and which will function, at least to some degree, to contain the wash of the propeller and thus enable the ship to be more efficiently operated with less fuel consumption.
Examples of various forms of ships' propellers other than conventional propellers and which have been designed to overcome some of the above noted inefficient operating characteristics of conventional ships' propellers are disclosed in U.S. Pat. Nos. 904,313, 2,328,041, 2,896,565, 3,115,112 and 3,828,713.